Calculating Final Angular Velocity of Turntable with Runner on a Horizontal Axis

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In summary, a 55 kg runner with a velocity of 3.1 m/s relative to the Earth is running around a horizontal turntable with a radius of 3.0 m and a moment of inertia of 120 kg-m2. The turntable is rotating in the opposite direction with an angular velocity of 0.20 rad/s relative to the Earth. To find the final angular velocity of the turntable when the runner slows to a walk and is at rest relative to the Earth, the equation ΔL = 0 is used, resulting in an answer of -4.06 rad/s.
  • #1
reminiscent
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Homework Statement


A 55 kg runner runs around the edge of a horizontal turntable mounted on a vertical, frictionless axis through its center. The runner's velocity relative to the Earth has magnitude of 3.1 m/s. The turntable is rotating in the opposite direction with an angular velocity of magnitude 0.20 rad/s relative to the earth. The radius of the turntable is 3.0 m, and its moment of inertia about the axis of rotation is 120 kg-m2. Find the final angular velocity of the turntable if the runner slows to a walk in such a way that she is at rest relative to the earth.

Homework Equations


ΔL = 0
L1 = L2

The Attempt at a Solution


This was ripped off from a problem in the book that asked for "the final angular velocity of the system if the runner comes to rest relative to the turntable," which I did just that, but I just noticed that this problem's last sentence is a different variation (final angular velocity of the turntable if the runner slows to a walk in such a way that she is at rest relative to the earth.")
Here is what I did - should I change anything at the end?
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  • #2
Your working is not easy to read (posting images is for diagrams and printed/typed matter) and you do not define your variables, which makes it hard to follow.
I get a different answer.
 
  • #3
haruspex said:
Your working is not easy to read (posting images is for diagrams and printed/typed matter) and you do not define your variables, which makes it hard to follow.
I get a different answer.
Well T stands for turntable and R stands for runner. L1 was the initial and L2 was the final. L1 consisted of the angular momentums of both the turntable and runner. I treated them as a system at the end having the same angular velocity.
 
  • #4
Can anyone tell me what I did wrong?
 
  • #5
haruspex said:
Your working is not easy to read (posting images is for diagrams and printed/typed matter) and you do not define your variables, which makes it hard to follow.
I get a different answer.
I got a new answer of -4.06 rad/s.
 
  • #6
reminiscent said:
I got a new answer of -4.06 rad/s.
That's right.
 

What is a runner on a turntable?

A runner on a turntable refers to an object, typically a human or animal, running on a circular platform that is able to rotate.

What are the factors that affect a runner on a turntable?

The factors that affect a runner on a turntable include the speed and direction of rotation of the turntable, the weight and size of the runner, and the friction between the runner's feet and the surface of the turntable.

How does a runner on a turntable maintain their balance?

A runner on a turntable maintains their balance by adjusting their body and center of gravity to counteract the centrifugal force caused by the rotation of the turntable. They also use their muscles and a combination of visual and sensory cues to stay upright.

What is the purpose of studying a runner on a turntable?

Studying a runner on a turntable can provide insight into the principles of inertia, centripetal force, and balance. It can also be used as a physical model to understand the effects of rotation and movement on the human body.

How does a runner on a turntable differ from a runner on a stationary surface?

A runner on a turntable experiences additional forces, such as centrifugal force, that can affect their movement and balance. They may also need to use different techniques and strategies to maintain their balance compared to a runner on a stationary surface.

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